[Telemetry] Don't create a new Tab object at each navigation.

tools/telemetry/telemetry/core/web_contents.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from telemetry.core import util
 
 DEFAULT_WEB_CONTENTS_TIMEOUT = 90
 
 # TODO(achuith, dtu, nduca): Add unit tests specifically for WebContents,
 # independent of Tab.
 class WebContents(object):
   """Represents web contents in the browser"""
   def __init__(self, inspector_backend):
     self._inspector_backend = inspector_backend
 
-  def __del__(self):
-    self.Disconnect()
-
-  def Disconnect(self):
-    self._inspector_backend.Disconnect()
-
   def Close(self):
     """Closes this page.
 
     Not all browsers or browser versions support this method.
     Be sure to check browser.supports_tab_control."""
     self._inspector_backend.Close()
 
   def WaitForDocumentReadyStateToBeComplete(self,
       timeout=DEFAULT_WEB_CONTENTS_TIMEOUT):
     self.WaitForJavaScriptExpression(
@@ skipping 54 matching lines @@
     return self._inspector_backend.timeline_model
 
   def StartTimelineRecording(self):
     self._inspector_backend.StartTimelineRecording()
 
   def StopTimelineRecording(self):
     self._inspector_backend.StopTimelineRecording()
 
   def TakeJSHeapSnapshot(self, timeout=120):
     return self._inspector_backend.TakeJSHeapSnapshot(timeout)